1. Field of the Invention
The present invention relates to a surface inspection method and an apparatus to inspect a film-coated inspection subject such as a wafer. For example, the present invention relates to a surface inspection method and an apparatus to inspect foreign particles or flaws, which exist on the surface of a semiconductor wafer having a film structure, by two or more kinds of laser.
2. Related Art
By inspecting the surface of a wafer for inspection, it is possible to indirectly control the status of manufacturing equipment that processed the wafer.
Conventionally, when inspecting the surface of a filmless wafer, it has been unnecessary to take the quality of the wafer itself into consideration because the reflectance at the wafer surface is substantially fixed.
For this reason, a calibration wafer, where reference grains whose grain diameter is known are coated on its surface by a predetermined number, is commonly used for each of different measurement to perform calibration, and thus it was possible to control accuracy.
Therefore, it is understood that the calibration by the calibration wafer has been used for controlling an inspection apparatus itself.
On the other hand, when a film-coated wafer is used as an inspection subject, an operator sequentially sets the inspection conditions or the like of the surface inspection apparatus for each wafer to be inspected so as to combine the conditions with the value of each parameter regarding the film on the wafer. Thus, the operator has set an optimum calibration curve used in the inspection.
Optical conditions such as surface reflectance, film refraction index, internal reflection, and the like vary due to the thickness and the quality of the film formed on the wafer. For this reason, it is required to stabilize inspection sensitivity taking the thickness and quality of the wafer itself, which is a measurement subject, in consideration. So, it is usually the case that the operator stabilizes the sensitivity by changing the condition settings regarding the wafer to be inspected for each measurement. Refer to the description of the prior art written in Japanese Patent Laid-Open No. 2001-281162.
For example, in the case of a wafer having a particular film structure such as a SOI wafer that has been used in recent years, the status of each wafer itself is strictly inspected. To set the optimum inspection sensitivity, light quantity and polarization are set as inspection data. At this point, the operator has manually set desired optical inspection conditions taking the interrelationship between the inspection data and film parameters (film type, film number, refraction index and the like) in thorough consideration. Such condition settings have been complicated and difficult for the operator and advanced knowledge and experience have been required.
As described, to perform the optimum surface inspection for the film-coated wafer, it has been necessary for the operator to properly set the conditions for each measurement while associating the film parameters (such as film thickness and refraction index) regarding the film on the wafer to be inspected with corresponding inspection data (such as wavelength of inspection light, polarization status, incident angle on wafer surface) of the inspection apparatus, in other words, with an optimum correlation.
Conventionally, the operator has manually entered to set the inspection data such as the wavelength of inspection light, polarization status and incident angle for each measurement based on the film parameters (film thickness and refraction index in particular) of the wafer to be inspected on the basis of a known mutual correlation.
For example, the operator has described the values of each film parameter in the form of a comma-delimitated text format data and had the inspection apparatus read the value.
However, such a condition settings operation by the operator is a complicated and difficult operation where he/she selects the optimum optical inspection conditions and sets the values while taking a plurality of film parameters in consideration. Only an experienced operator can properly execute the operation. Additionally, the operation has overloaded even the experienced operator.
Further, in the surface inspection apparatus, when it is impossible to switch (or mix) the wavelengths on one apparatus and one incident angle, it has been difficult to set the inspection conditions of the inspection apparatus to the optimum conditions with respect to the film thickness and film refraction index of the wafer to be inspected.
Furthermore, when changing the configuration or the settings of the apparatus, it has been impossible to automate the settings for the wavelength of the inspection light and the polarization of incident angle corresponding to the film thickness and film refraction index of the wafer to be inspected.